#include <iostream>
#include <math.h>
using namespace std;
int main()
{
	double a,b,c,d=0;
	double p,s;
	cout<<"a=";cin>>a;
	cout<<"b=";cin>>b;
	cout<<"c=";cin>>c;
	p=(a+b+c)/2.0;
	s=sqrt(p*(p-a)*(p-b)*(p-c));
	cout<<s<<'\n';
	return 0;
	
}
